Water for town supply is chlorinate to make it free from

Step 1: Analyze the question The question asks what the purpose of chlorinating town water supply is. In other words, what does chlorine remove or eliminate from the water?

Step 2: Explain the concept Chlorination is a stage in water treatment where chlorine (or chlorine compounds such as bleaching powder) is added to water. Chlorine is a strong oxidizing agent and a disinfectant. It kills disease-causing microorganisms such as bacteria, viruses and other germs, so that the water is safe to drink and does not spread diseases like cholera, typhoid and dysentery.

Step 3: Go through the options

• A. Bad colour: Colour is not mainly removed by chlorine. It is dealt with by filtration, coagulation (using alum) and aeration. Chlorine is not used for this purpose.
• B. Bacteria: Chlorine kills bacteria. This is its main purpose in water treatment.
• C. Temporary hardness: This is caused by dissolved calcium or magnesium hydrogen carbonate. It is removed by boiling or by adding slaked lime (Clark's method), not by chlorine.
• D. Permanent hardness: This is caused by calcium or magnesium sulphates and chlorides. It is removed by adding washing soda (sodium carbonate) or by ion exchange (e.g. permutit), not by chlorine.

Step 4: Answer Chlorination makes water free from bacteria, which is option B.

Exam tip: Remember the water treatment order and the job of each stage:

• Sedimentation/coagulation (alum) → removes suspended particles
• Filtration → removes remaining solids
• Chlorination → kills germs (bacteria)

Whenever you see "chlorine" and "water supply" together, think "kills germs".